
Two-sample t test with equal variances
------------------------------------------------------------------------------
   Group |     Obs        Mean    Std. Err.   Std. Dev.   [95% Conf. Interval]
---------+--------------------------------------------------------------------
 control |  17,281    21804.11    174.9406    22997.21    21461.21    22147.01
experime |  17,281    21844.13    171.2961    22518.11    21508.37    22179.89
---------+--------------------------------------------------------------------
combined |  34,562    21824.12    122.4182     22758.6    21584.18    22064.06
---------+--------------------------------------------------------------------
    diff |           -40.01756    244.8399               -519.9118    439.8767
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    diff = mean(control) - mean(experime)                         t =  -0.1634
Ho: diff = 0                                     degrees of freedom =    34560

    Ha: diff < 0                 Ha: diff != 0                 Ha: diff > 0
 Pr(T < t) = 0.4351         Pr(|T| > |t|) = 0.8702          Pr(T > t) = 0.5649
